Recent studies of aerosols originating from marine environments have found that several cations are enriched at the aerosol surface relative to the bulk core. Organic compounds, such as lipids, are also typically found at the interface of aerosols. A fundamental understanding of the interactions of cations with insoluble lipids is necessary, as the organization and structure of the interfacial region controls the reflectivity and reactivity of the aerosol. Yet, studies of lipid films on highly concentrated salt solutions have not been previously reported. In the study presented here surface pressure-area (π-Area) isotherms and Brewster angle microscopy (BAM) were used to monitor the effect of cation enrichment (Na+, K+, Mg2+, Ca2+, Sr2+, Zn2+) on the interfacial organization of dipalmytiolphosphatidylcholine (DPPC). Concentration of the salt solution was varied to model aerosols with salt concentrations that naturally occur (0.3 M) to super-saturated conditions (2.0 M). Results reveal that packing of the monolayer depends on the identity of the cation, and that the expansion or condensation of the monolayer is enhanced with increasing concentration. Imaging of the surface morphology indicates that divalent cations interact with DPPC molecules more strongly than monovalents, where the binding affinity has the following trend: K+ &lt; Na+ &lt; Mg2+&lt; Sr2+&lt; Ca2+&lt; Zn2+ Independent of cation, fluidization of the monolayer occurs when cations become highly enriched in the surface region (&gt; 2.0 M). Results reported here indicate that the interfacial organization of a DPPC monolayer differs drastically when cations are highly concentrated, giving rise to a surface that more strongly resembles a bare salt solution than an organic monolayer.

Effect of cation enrichment on the organization of a DPPC monolayer at the air-aqueous interface

251st National Meeting (2016)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.